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transistor help needed
开云体育Hi Paul, ? Look for their datasheets. AOD472 is rated at 50A with an RDSon of 0,0095 Ohm BUZ72A is rated at 11A with an RDSon of 0,25 Ohm ? What this tells you is, the BUZ72A is only able to handle about 1/5th of the total current. It also has a much higher internal resistance when turned on (RDSon), meaning it will heat up a lot more for the same amount of current. No idea what those MOSFET’s are handling, but you’re looking at a possible “cloud of smoke” for each BUZ. Only advantage I see on those BUZ is their higher voltage handling. Which partially explains the downside with current. ? AOD472 is rated at 25V. Use this parameter to look for a good replacement in that package you want. Generally speaking, the lower the voltage rating, the higher the current handling. RDSon varies wildly from device to device (along with price…), a lower RDSon (internal resistance when on), means lower heat generation, and smaller heatsinks. ? Can’t remember any of the top of my head, supplier websites usually have a search tool with filters, where these parameters are selectable. ? Nuno T. ? ? From: [email protected] [mailto:[email protected]] On Behalf Of paul larner via groups.io ? would a buz 72a be ok for a replacement? -- Nuno T. |
开云体育24V stepper motors driven by 25V rated MOSFET’s is a really bad idea. That’s too close to the their limit. A single coil spike could destroy them. From this perspective, The BUZ seems a better option. I’m assuming those stepper motors will not consume anywhere near 11A. As long as they have a good heat sink assembly, it’s worth a try. If you’re going to buy them on purpose, I advise looking for something better. If you already have them, and assuming a hand size stepper motor, 11A seems more than enough. ? So, yes, they might work. (I assume no responsibility for any smoke clouds! :D ) ? Nuno T. ? From: [email protected] [mailto:[email protected]] On Behalf Of paul larner via groups.io ? well at the moment aan arduino uno is driving the aod472 fets to drive a nima 23 stepper,i have made a pcb in eagle the buz 72 would be better to mount on the pcb than the d2pak fets,i just wondered if they would work,i am using 24v for the stepper. -- Nuno T. |
开云体育OP should also be aware of drive limitations of the Arduino pins. Transition times (off-to-on and on-to-off) can be very high power dissipation times, even more than on times. Donald. Sent from Proton Mail Android -------- Original Message -------- On 11/23/24 09:52, Nuno Yahoo wrote:
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开云体育Indeed. I do not know how an Arduino board is made, but a MOSFET gate driver is something to consider. ? Something like this: There’s plenty of options around. ? Nuno T. ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Donald H Locker via groups.io ? OP should also be aware of drive limitations of the Arduino pins. Transition times (off-to-on and on-to-off) can be very high power dissipation times, even more than on times. Donald. Sent from Proton Mail Android
24V stepper motors driven by 25V rated MOSFET’s is a really bad idea. That’s too close to the their limit. A single coil spike could destroy them. From this perspective, The BUZ seems a better option. I’m assuming those stepper motors will not consume anywhere near 11A. As long as they have a good heat sink assembly, it’s worth a try. If you’re going to buy them on purpose, I advise looking for something better. If you already have them, and assuming a hand size stepper motor, 11A seems more than enough. ? So, yes, they might work. (I assume no responsibility for any smoke clouds! :D ) ? Nuno T. ? From: [email protected] [mailto:[email protected]] On Behalf Of paul larner via groups.io ? well at the moment aan arduino uno is driving the aod472 fets to drive a nima 23 stepper,i have made a pcb in eagle the buz 72 would be better to mount on the pcb than the d2pak fets,i just wondered if they would work,i am using 24v for the stepper.
Nuno T. -- Nuno T. |
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As a first approximation, driving a MOSFET's gate means driving into a big capacitance.? The bigger/stronger the FET, the bigger is that capacitance.? It can be quite large, and part of it is from gate to drain where it may be multiplied by Miller effect.
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Driving capacitance gives you (as a first approximation) an RC low-pass filter, meaning that the MOSFET's gate voltage rises or falls much more slowly than the nominal rise and fall times of the driving device if it had no load.
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Hopefully you take that into account.? That is where those MOSFET gate drivers help.
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Andy
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Need to work backwards in any design to the input requirements. How much voltage is the output being driven? What is the start-up current of the motor being driven? Now you can select the MOSFET size. You do not necessarily need a MOSFET that can drive a Tesla motor. Now, think about how much current that MOSFET needs. Do you want to put a series resistor on the gate to help control EMI concerns? If you are over-driving the output of the Arduino, think about inverting the signals and use a smaller MOSFET to drive the gate of the larger one.
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I have spent 30+ years designing stuff from small commercial electronics to motor drivers going into space; plus over a decade in the semiconductor industry as senior apps engineer and market development. If my considerations are not thought of in advance, you will learn that genies inside electronics can be released.;-)
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DerekK
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On Sunday 24 November 2024 10:47:17 am sdmonaco via groups.io wrote:
Hi Paul, these are what I like to use.Hmm. A 2-pack for around $10, or a 5-pack for around $15...? I know which I'd go for. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
Derek Koonce